1. Field of the Invention
The present invention relates to a print head and an image forming apparatus including the same, and more particularly, to a print head having a liquid crystal polymer microlens array, and an image forming apparatus including the print head.
2. Description of the Related Art
In order to form an image, a conventional electrophotographic image forming apparatus scans light on a photoconductor charged with a predetermined potential, forming an electrostatic latent image thereon, develops the electrostatic latent image by supplying a developer (toner) from a developing roller spaced apart from the photoconductor so that the developer selectively adheres on the photoconductor according to the potential level thereof, transfer the developed image on a sheet of paper, and fixes the image on the sheet of paper.
Such electrophotographic image forming apparatus includes a laser scanning unit for scanning a laser beam on the photoconductor. However, the laser scanning unit requires a highly precise optical arrangement, and can be very expensive.
As a way of realizing an image forming apparatus without a laser scanning unit, a print head having a structure as shown in FIG. 1 has been suggested.
Referring to FIG. 1, a conventional print head of this type includes a semiconductor light emitting device (hereinafter, referred to as an LED) array 1, which includes a plurality of LEDs, and a SELFOC lens array 5, which condenses light emitted from each of the LEDs of the LED array 1 so as to form an image corresponding to the light from each LED incident on the photoconductor. A SELFOC lens is a type of gradient index (GRIN) lens that operates by ion exchange, for example, an ion exchange between SiO2 and Ag.
Each of the LEDs that forms the LED array 1 are independently turned on/off by a predetermined current level supplied by a driving chip 3 according to an image signal received from a main controller. Light emitted from an LED is condensed in the SELFOC lens array 5 and projected onto the photoconductor so as to form a latent image 7.
When the conventional print head forms the latent image 7 on the photoconductor by turning on/off the LEDs according to the input image signal, the amount of light emitted by each LED may vary. To compensate for the variation of the light output each time a line is scanned in the main scanning direction, each LED is turned on/off with reference to a preset current level corresponding to the respective LED, thereby making the amount of light emitted by each LED uniform. However, this complicates the configuration of a driving circuitries. Further, if the current consumption changes suddenly according to the input image signal, such as when white lines are scanned immediately after black lines had been scanned, a surge effect may be generated, and thus the driving circuit may become damaged.
Another alternative way of realizing an image forming apparatus without a laser scanning unit is disclosed in U.S. Pat. No. 6,825,865, entitled “PRINT HEAD WITH LIQUID CRYSTAL SHUTTER.”
A print head disclosed in U.S. Pat. No. 6,825,865, includes a white light source or red, blue, and green light sources, and a liquid crystal shutter for each light source, and is configured to transmit red, blue, and green lights to the corresponding regions of a photoconductive film according to an input voltage. Light transmitted through the liquid crystal shutter is transmitted through a SELFOC lens array via a reflector and then transmitted through a prism to form an image on a photosensitive film.
Since the print head uses a SELFOC lens array and a prism for securing an optical path and for focusing, the mechanical and optical structures of the print head are complicated. Also, since a SELFOC lens is very expensive, the manufacturing costs of the print head thus also increase.